But one thing addiction counselor Neal Hayden knows for sure: Marijuana users can become dependent on the drug, and there’s no way to tell for sure who’s at risk.

Hayden owns Gateway Behavioral Health on East Third Avenue in Spokane. He started the program after working for a decade in the chemical dependency program at Deaconess Medical Center.

While some people can use cannabis with no negative effects – like others use alcohol – about 5 percent cross a line, he said.

“People become dependent on it to cope emotionally,” Hayden said. “If they use it long enough, they become physiologically dependent on it.”

Regular users – most use around a gram daily – who try to quit suffer physical symptoms such as severe headaches and psychological symptoms such as anxiety and depression along with “a basic sense of restlessness and irritability,” Hayden said. Relapse rates are high.

Why some regular users grow dependent while others don’t is “a great mystery,” Hayden said, but it probably has to do with their fundamental brain chemistry.

All “substances of abuse” mimic a natural neurochemical, he explained. Alcohol mimics one, and opiates another. Cannabis mimics another. If you use enough, your brain shuts off natural production. And when you cut off the outside supply, it takes awhile for the brain to produce it again.

The question is whether you’ve permanently impaired your brain’s ability to produce enough. Some brains never can, causing depression or restlessness or psychosis or irritability.

Among signs of dependency: Users use more than they intend for longer than they intend. They try and fail to cut down and or halt their use.

A responsible recreational pot smoker might never suspect they’d be at risk for dependence.

Marijuana sold to recreational users under Initiative 502 must carry a warning of its “habit forming” potential, under regulations released this month.

Among other health warnings required by labeling regulations:

• “Smoking is hazardous to your health.”

Because marijuana has been so heavily controlled by the federal government, research on its health effects has been limited.

But studies examining cancer risk have been “pretty positive,” showing marijuana smokers face less cancer risk from smoking than cigarette smokers, said Dr. Kim Thorburn, who ran the Spokane Regional Health District from 1997 to 2006 and advocated for I-502.

However, “whether that has to do with the fact that it’s not smoked as heavily as nicotine and cigarettes isn’t really worked out,” she said.

Just in case, take a look at vaporizers to reduce the risk of lung damage from smoke, advised Roger Roffman, a professor emeritus of social work at the University of Washington and longtime marijuana policy activist.

• Labels on marijuana “must include concentration of THC, THCA, CBD, including a total of active cannabinoids.”

Cannabinoids, the chemical substances made by the cannabis plant, are key to how it makes the user feel. Selective breeding of the plants has increased potency in the past few decades, according to an “information for the consumer” packet compiled by UW’s Roffman. Very high THC consumption might be dangerous for some people.

Like a “proof” label on alcohol, marijuana’s “potency profile” can give a user an idea of what they’re getting into, said the Liquor Control Board’s Randy Simmons.

“The downside, which was not addressed by the initiative, is ‘What does that mean? What does 14 percent mean compared to 10 percent?’ ” Simmons said. “There’s been no studies done based on gender, height, weight, age of what the impact is.”

Simmons said he wouldn’t encourage anyone to start smoking.

“But if I was,” he said, “I would encourage them to start out low and figure out how it impacts you. And if you want something stronger, your choice is to go find something stronger.”

• “Keep out of reach of children.”

I-502 limits legal recreational use to those 21 and older.

Parts of the brain may not develop the way they’re supposed to in teens who smoke a lot of pot, Roffman said. The results – memory and learning problems, difficulty making plans and solving problems – could be permanent.